The invention relates generally to electronic locking systems and deals more particularly with a card reader for reliably reading data from key cards.
U.S. Pat. No. 4,126,780 discloses an optical card reader having a spring to bias the card away from the light detector and a photo-electric bottom detector to produce a signal when the card reaches the bottom of the reader.
U.S. Pat. No. 4,519,228 discloses an electronic recodeable lock which includes a magnetic or optical card reader. The card reader includes a lever activated switch which turns on the reading head when the key is inserted into the slot and an end switch which turns the reading head off when the key reaches the end of the slot.
U.S. Pat. No. 3,896,293 discloses a card reader having a constant velocity card transport mechanism. This reader utilizes a cantilever spring to urge a roller against the card so that the coded portion of the card will be forced against the read head.
U.S. Pat. No. RE29,846 discloses an electronic lock system which includes a key card reader. This card reader contains a microswitch to activate the read sensors after the card has been fully inserted.
U.S. Pat. No. 3,622,,991 discloses an electronic locking system which includes an optical card reader system. This card reader utilizes a shutter which is capable of limited pivotal movement to insure correct orientation of the key card in the slot.
In addition, various cyclical redundancy checking (CRC) processes were previously known to determine whether data read from a disc drive or data tape system is true. The CRC data is stored on the disc drive or tape along with the data. Such data was read at constant velocity in one direction as the tape or disc was driven by a machine process. Also, a linear redundancy checking (LRC) process was previously known to determine whether data stored on a credit card was true. The LRC was performed as data was read in one direction and comprised a parity bit for each of the data bits.
Problems presented by prior art card readers, such as those described above, include misreading the data contained on the cards. Such problems are particularly troublesome for card readers utilized for electronic door locks because the insertion of the correct card key will not result in opening the lock.
Misreading may be caused by a misalignment of the card with the read head. In addition, misreading may occur because the card does not move past the read head at adequate velocity. Also, misreading may be due to start-up conditions. If a key card contains a serial magnetic track, it may be difficult to read the first bit on the track, as discussed in more detail below.
It is an object of the present invention to provide a card reader that reliably reads data on the cards.